Doc/memory-hotplug.txt: corrections and callback function prototype

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8. Memory hotplug event notifier

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Memory hotplug has event notifier. There are 6 types of notification.

Hotplugging events are sent to a notification queue.

MEMORY_GOING_ONLINE

There are six types of notification defined in include/linux/memory.h:

MEM_GOING_ONLINE

  Generated before new memory becomes available in order to be able to

  prepare subsystems to handle memory. The page allocator is still unable

  to allocate from the new memory.

MEMORY_CANCEL_ONLINE

MEM_CANCEL_ONLINE

  Generated if MEMORY_GOING_ONLINE fails.

MEMORY_ONLINE

MEM_ONLINE

  Generated when memory has successfully brought online. The callback may

  allocate pages from the new memory.

MEMORY_GOING_OFFLINE

MEM_GOING_OFFLINE

  Generated to begin the process of offlining memory. Allocations are no

  longer possible from the memory but some of the memory to be offlined

  is still in use. The callback can be used to free memory known to a

  subsystem from the indicated memory block.

MEMORY_CANCEL_OFFLINE

MEM_CANCEL_OFFLINE

  Generated if MEMORY_GOING_OFFLINE fails. Memory is available again from

  the memory block that we attempted to offline.

MEMORY_OFFLINE

MEM_OFFLINE

  Generated after offlining memory is complete.

A callback routine can be registered by

A callback routine can be registered by calling

  hotplug_memory_notifier(callback_func, priority)

The second argument of callback function (action) is event types of above.

The third argument is passed by pointer of struct memory_notify.

Callback functions with higher values of priority are called before callback

functions with lower values.

A callback function must have the following prototype:

  int callback_func(

    struct notifier_block *self, unsigned long action, void *arg);

The first argument of the callback function (self) is a pointer to the block

of the notifier chain that points to the callback function itself.

The second argument (action) is one of the event types described above.

The third argument (arg) passes a pointer of struct memory_notify.

struct memory_notify {

       unsigned long start_pfn;

If status_changed_nid* >= 0, callback should create/discard structures for the

node if necessary.

The callback routine shall return one of the values

NOTIFY_DONE, NOTIFY_OK, NOTIFY_BAD, NOTIFY_STOP

defined in include/linux/notifier.h

NOTIFY_DONE and NOTIFY_OK have no effect on the further processing.

NOTIFY_BAD is used as response to the MEM_GOING_ONLINE, MEM_GOING_OFFLINE,

MEM_ONLINE, or MEM_OFFLINE action to cancel hotplugging. It stops

further processing of the notification queue.

NOTIFY_STOP stops further processing of the notification queue.

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9. Future Work

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